Recovery of solvent from hydrocarbon oils



RECOVERY oF soLvEN'r FROM HYDRO- oAnBoN oiLs .lames H. McCullough, Philadelphia, Pa., assignor to The Atlantic Refining Company, Phila.- delphia, Pa., a corporation of IPennsylvania Application January 24, 1940, Serial No. 315,337

' (ci. iss- 32) 6 Claims.

e The present invention relates to a method of recovering residual solvent from hydrocarbon oil, and relates more particularly to a method of recovering methanol from hydrocarbon oil whichhasbeen treated with a solution of an alkaline reagent in methanol for the removal of sulfur compounds from said oil.

My invention is especially adapted for use in conjunction with the oil refining process disclosed and claimed in U. S. Patent-'#1,968,842 to Malisoi, which process comprises treating a mercaptan-containing oil with a. solution of an alkaline reagent in an organic solvent, thereby to convert the mercaptans into mercaptides soluble in the solvent, and separating the solution from the treated oil. While a solution of sodium hydroxide in methanol is the preferred treating agent, other alkaline reagents and other solvents may be suitably employed. Preferably the treating agent is substantially immiscible with the oil to be treated, or may be rendered so by the addi--H` tion oi' small quantities of water or other substances.

In carrying out the oil rening process disclosed by Malisoi'l, the mercaptan-containing oil is intimately contacted with a small volume of a treating agent comprising, for example, a sodium hydroxide saturated solution of methanol containing 10% by volume of water. The mercaptan content of the oil is thereby converted into sodium mercaptides which are preferentially soluble in the treating agent. The spent solution of treating agent containing the mercaptides is then separated from the oil by decantation, and the solution may thereafter be subjected to treatment for the recovery of the mercaptans and the regeneration of the sodium hydroxide. Such treatment may consist in removing sub' stantially all of the methanol by fractional dis tillation, and then heating the residue comprising water, unreacted sodium hydroxide, and sodium mercaptides, preferably in the presence of steam, to hydrolyze the mercaptides to mercaptans and sodium hydroxide, and removing the water and mercaptans by distillation to produce as a final distillation residue, a concentrated aqueous solution of regenerated sodium hydroxide.

Hydrocarbon oils treated for the removal of sulfur compounds in accordance with the patented process have been found to retain small but appreciable amounts of solvent, l. e.. methanol. It is possible to remove the residual methanol from the oil by water washing, but considerable quantities of water are necessary, and the cost of separating the methanol from the Water makes such method oi recovery uneconomical and v.therefore impractical.

Ihave found that the residual methanol retained in the treated oil may advantageously be tic-methanol solution, is passed from makedip I recovered therefrom by contacting or washing such oil with an aqueous alkaline solution, and preferably a concentrated aqueous solution of sodium hydroxide such as that recovered in the regeneration of the spent treating agent above described. By operating in accordance with my invention, I am able to remove substantially all of the methanol retained in the treated oil in such a manner that the recovered methanol and the concentrated sodium hydroxide solution employed in such recovery may be utilized directly in preparing a regenerated treating agent for reuse in the treatment of additional quantities of mercaptan-containing oil.

My invention may be further understood with reference to the accompanying drawing, which illustrates diagrammatically a system suitable for carrying out my recovery method.

Referring to the drawing, mercaptan-containing hydrocarbon oil, such as sour gasoline distillate, is introduced by means of valve-controlled .pipe l into the lower section of contacting tower 2 provided with perforated bailles 3 or other suitable packing material. Treating agent, for example, methanol saturated witl' sodium hydroxide, and hereinafter termed caustank 4 through pipe 5, and is pumped bypump t, through pipe 'l into the upper section of the contacting tower 2. The quantity of causticmethanol solution to be employed varies with the quantity of distillate to be treated, the sulfur content of the distillate, and the conditions under which the treatment is carried out, but is generally of the order of from about 2% to about 10% by volume of the distillate. The sour gasoline distillate,- being of lower specific gravity than the caustic-methanol solution, passes upwardly through the tower in intimate countercurrent contact with the descending ow of solution, and the mercaptan content of the distillate is thus converted into sodium mercaptides which are preferentially soluble in the caustic-methanol solution. Spent solution, lsubstantially freey ofA distillate, and comprising 90% methanol, unreacted caustic, sodium mercaptides, and traces of tarry matter and phenoliccompounds, is with!- drawn from the bottom of tower 2 and is passed by means oi valve-controlled pipe 8 to a heating device such as a steam jacketed coil 9, wherein the temperature of the spent solution is' raised, for example, to about 200 F. 'I'he heated solu-y tion is then introduced by means of pipe l0 into a suitable iractionating column il provided with bubble trays i2, heating coil i3, and dephlegmating coil I4. Herein the spent solution is fractionated to separate the methanol from the water, caustic, mercaptides, tar and phenolic .come pounds, the temperature within the column being' controlled to prevent substantial decon'ipositioiil drawn from the bottom of column H, at a tem v perature of, for example, 225 l". to 250 1"., and is passed by pipa 24 into tank 2|, from which it is pumped by pump 22 through pipe 23 into ay hydrolyzing tower 24 provided with bubble trays 25, heating coil 2i, steam jet 21, and dephlegmating coil 2l. The solution in passing downwardly through the tower is subjected to additional heating, preferably by means of steam introduced at the bottom of the tower through jet 21, whereby the sodium mercaptides are hydrolysed to free mercaptans and caustic soda is regenerated. Ii' desired, the steam supplied through :et 21 maybe dispensed with, and in lieu thereof, heating may be effected by circulating steam or other heating medium throughA the heating coil 2l. The merca-ptans and a portion of the water content of the solution are vaporized and pass upwardly through the tower, at least a portion of the water vapors being condensed by ,the dephlegmating coil 2l in the top of the tower. The vaporized mercaptans and water vapors passing the dephlegmating coil 2l are conducted from the top of the tower by pipe 28 and passed to condenser wherein the vapors are condensed, the liquid condensate being passed by means of pipe Si to separator 42. The mercaptans and water, being substantially immiscible with one another, are permitted to stratify into two layers in the separator, the mercaptans being withdrawn from the upper portion of the separator I2 through valve-controlled pipe 34 and disposed of as deaired. The water is withdrawn from the bottom of the separator I2, and a portion thereof may be returned to the upper section of tower 24 by means of valve-controlled'pipe n, the remainder being removed from the system through valveco'ntrolled pipe 33'. In the event that heat is supplied by heating coil 20, and open steam is not utilized, all of the water separated from the mercaptans in separatorI i2 may be returned to the tower 24 by means of valve-controlled pipe 33. `The separator may be vented, when necessary, by means of valve-controlled pipe Il. By properly controlling the operation of the hydrolyzing tower, the mercaptans may be substantially separated from the water, unreacted caustic and regenerated caustic, tarry matter and phenolic compounds. This aqueous solution, which may contain from about 40% to about 50%' of caustic soda, together with the terry matter and phenolic compounds, is passed from the bottom of tower 24, at a temperature oi, for example, 285 F., and under super-atmospheric pressure, through valve-controlled pipe 36 into tank 3l, the tarry matter being permitted to stratify and collect in `the upper portion of the tank, from which it may be withdrawn, when necessary, by means of valve-controlled pipe 3l. Since a portion of the caustic soda content of the solution may eventually be converted into sodium suliide or other stable salts during use in the system, a quantity of the solution may be periodically removed from the system through ancona? rate or precipitate from the cooled solution This mixture is then passed from the cooler 42 through pipe 4l into separator 44, wherein the precipitatedv phenolic compounds and/or tarry matter is separated from the solution and drawn from the top oi the separator by means of valvecontrolied pipe 4l. The cooled solution, comprising substantially a concentrated @09E-50%) aqueous solution of regenerated caustic soda, is passed from the upper portion of separator 44 throughv valve-controlled pipe 5l into the upper section of contacting tower 4I provided with per forated baiiles 41, or other suitable packing material.

Gasoline distillate containing small amounts of methanol is withdrawn from the' top oi.' tower I' and passed by means of pipe 44 into the lower section of tower 46. Since the speciic gravity of the distillate is lower than that of the regenerated caustic aoda solution introduced into the upper section of tower 48, the distillate flows upwardly through the tower in intimate countercurrent contact with the descending now of caustic solution, whereby the methanol content of the distillate is extracted by and dissolved in the caustic solution. The gasoline distillate, subv stantially free of methanol, is passed from the top of tower 4l through valve-controlled pipe 4I to storage (not shown). late may be subjected to water washing prior to storage or other disposal thereof.

The caustic soda solution containing methanol extracted from the gasoline distillate is withdrawn from the bottom of tower 48 and is passed by means of valve-controlled pipe l0 into' make-up tank 4, wherein it may be admlxed with methanol from the initial fractionation in column H. The make-up tank 4 may be pro vided with valve-controlled pipes 5| and I2, whereby i'resli'methanol and caustic solution, respectively, may be supplied to the make-up tank, as required. Ii desired, fresh vcaustic solution may be supplied to the uppe'r'section of tower 4| by means of valve-controlled pipes I3 and Il, although it is preferred to employ regenerated caustic solution for the extraction of residual methanol from the distillate supplied to tower 4i.

While, in thel system described above, I have shown the use of a single tower provided with per-v forated bailles for effecting counter-current extraction of distillate with the caustic solution, I may employ any other suitable means for obtaining intimate contact between the distillate and solution, for example, one or more towers filled with packing material, or an extraction system o1 one or more stages each comprising a mixing tank and a settling tank. Other modifications of thc apparatus comprising my recovery system are considered'within the scope of my invention.

Typicalof the results which may be obtained in accordance with my invention are the following:

(1) Uncracked petroleum naphtha containing 1.07% by volume of methanol was extracted with regenerated aqueous caustic soda solution oi' 50% If desired, the distilaqueous caustic soda solution of 45% strength,-

the caustic solution being applied in 1 treat of 1% by volume. The naphtha, after extractive treatment, was found to contain 0.011% methanol.

Hereinabove I have described the application of my invention in the recovery of methanol from gasoline distillate which has been treated with caustic-methanol solution for the removal of sulfur compounds. It is to be understood, however, that my invention is equally applicable to the recovery of solvents other than methanol which may be used in conjunction with alkaline reagents, and particularly the hydroxides, alkoxides, and carbonates of the alkali metals. Solvents such as ethyl, propyl, and isopropyl alcohols, glycols, glycerine, acetone, ethyl methyl ketone, dimethyl ketone, epichlorhydrin, and the like, may be suitably recovered from hydrocarbon oil in accordance with my method. Various modifications of the operating temperatures and pressures may be made, according to the nature and properties of the solvent to'be recovered. In some instances, and particularly in the case of high boiling solvents such as glycol or glycerine, sub-atmospheric pressures may be advantageously employed in certain stages of my recovery process, in order to maintain the operating temperature Within the desired range.

What I claim is:

1. In a process of removing mercaptan compounds from hydrocarbon oil involving contacting the oil with caustic methanol solution to form mercaptides soluble in said solution, separation of the mercaDtide-containing solution from the oil, removal of methanol from the mercaptidecontaining solution, and treatment of the resultant solution to decompose the mercaptides and produce an aqueous solution of regenerated caustic soda substantially free oi mercaptides, the method of recovering residual methanol from the treated oil, which comprises contacting said oil with said aqueous solution of regenerated caustic soda to extract from said oil residual methanol.

2. Iny a process of removing mercaptan compounds from hydrocarbon oil involving `contacting the oil with caustic methanol solution to form mercaptides soluble in said solution, separation Vo1.' the mercaptide-containing solution from the oil. removal of methanol from the mercaptidecontaining solution, and treatment oi the resultant solution to decompose the mercaptides 3. In a process oi removing mercaptan compounds from hydrocarbon oil involving contactfrom the mercaptide-containing solution ing the oil with caustic methanol solution to form mercaptides soluble in said solution, separation of the mercaptide-containing solution from the oil, removal of methanol from the mercaptide-containing solution, and treatment of the resultant solution to decompose the mercaptides and produce an aqueous solution of regenerated caustic sodasubstantially free of mercaptides, the method of recovering residual methanol from the treated oil, which comprises contacting said oil with said aqueous solution oi regenerated caustic soda to extract from said oil residual methanol, separating from the oil said aqueous solution containing extracted methanol, and admixing said solution with methanol recovered first mentioned.

4. In a process of removing mercaptan compounds from hydrocarbon oil involving contacting the oil with caustic methanol solution to form mercaptides soluble in said solution, separation of the mercaptide-containing solution from the oil, removal of methanol'i'rom the mercaptidecontaining solution, and treatment of the resultant solution to decompose the mercaptide's and produce an aqueous solution of regenerated u and produce an aqueous solution of regenerated caustic soda substantially free oi' 'mercaptidea the method of recovering residual methanol from the treated oil, which comprises contacting said oil with said aqueous solution of regenerated caustic soda' to extract from said oil residual methanol, separating from the oil said aqueous solutioncontaining extracted methanol, admixing said solution with methanol recovered from the mercaptide-containing solution first mentioned, and recirculating the resulting solution. for the treatment of additional quantities ofi mercaptan-containing oil.

5. In a process of removing mercaptan compounds from hydrocarbon oil involving contacting the oil with a solution comprising a lower aliphatic alcohol and an alkali metal hydroxide to form mercaptides soluble in said solution. separation of the mercaptide-containing solution from the oil, removal of the alcohol from the. mercaptide-containing solution and treatment of the resultant mercaptide-containing solution to decompose the mercaptides and to produce an laqueous solution of regenerated alkali metal hydroxide. the method of recovering residual lower aliphatic alcohol from the treated oil, which com4` prises contacting the treated oil with said aqueous solution oi regenerated alkali metal hydroxide to extract from said oil residual lower aliphatic alcohol.

6. In a process oi' removing mercaptan compounds i'rom hydrocarbon oil involving contactins' the oil with a solution comprising a lower aliphatic alcohol and an alkali-metal hydroxide to form mercaptides soluble in said solution, separation of the mercaptide-containing solution from the oil and treatment of the mercaptidecontaining solution to produce an aqueous solution of regenerated alkali metal hydroxide. the method of recovering residual lower aliphatic alcohol from the treated oil which comprises contacting the treated oil with said aqueous solution of regenerated alkali metal hydroxide to extract from said oil residual lower aliphatic oil.

JAMES H. MCCULLOUGH. 

